Pyrolysis gasoline is the by-product of steam cracking to make ethylene, which approximately comprises more than 50% of the production capacity of ethylene. Pyrolysis gasoline contains highly unsaturated hydrocarbons, such as diolefin, styrene and the like, which can be converted into corresponding monoolefin by selective hydrogenation. With the increasing ethylene production capability in China, the hydrogenation of pyrolysis gasoline has developed toward the hydrogenation of full distillate using nickel-based catalyst. Due to the variability of the pyrolysis gasoline raw materials and the differences in pyrolysis apparatus and pyrolysis modes, the pyrolysis gasoline raw materials are deteriorated, and the hydrogenation load and the content of impurity such as arsenic are increased, thereby causing the inferior performance of palladium-based catalyst for first-stage hydrogenation. For noble metal catalyst, its arsenic and colloid resistance as well as water resistance is low, since the impurity arsenic tends to occupy the empty orbital of Pd, and Pd is located on the surface layer of the catalyst with a content of only parts per thousand. For non-noble metal catalyst, it has certain arsenic tolerance and colloid and water resistance due to the structural difference and high metal content; moreover, it has relatively remarkable price advantage. Thus, there is need of the market and technical competition to develop a new nickel-based catalyst for first-stage hydrogenation of full distillate pyrolysis gasoline.
U.S. Pat. No. 3,472,763 reports a Ni/Al2O3 catalyst for the selective hydrogenation of diolefin, comprising 1-20% nickel as active component, 1-5% MoO3 as aids, 1-5% alkali metal and alkaline earth metal as aids, and having a pore volume of more than 0.4 ml/g and a specific surface area of more than 30 m2/g. This catalyst is prepared by impregnating the Al2O3 carrier with the aqueous solution of above-mentioned active component and aids. CN1218822A reports a Ni/Al2O3 catalyst suitable for the selective hydrogenation of pyrolysis gasoline distillates. This catalyst is prepared by loading nickel on alumina carrier comprising lithium or alkaline earth metal. However, this catalyst is not good at withstanding the hydrogenation load and its hydrogenation stability is to be improved.
An excellent selective hydrogenation catalyst should have higher hydrogenation activity and better selectivity. More importantly, it should have good stability. That is to say, it is necessary for such catalyst to have capability to resist impurity and colloid, thereby prolonging its lifetime.